The present invention relates to coating compositions which are curable and which can be used on transparent solid substrates. These coating compositions contain novel silanes which allow for dyeing and/or tinting (hereinafter "tintability") of such solid substrates. The curable coating compositions, containing the novel silanes, not only allow tintability, but these coating compositions also give excellent abrasion resistance, antifog and antistat properties to the coated article. In addition, the coatings described herein give very aesthetically pleasing, uniform, gel-free surfaces to the coated article.
Plastic materials, especially clear, transparent plastic materials, have been used in increasing amounts for various applications where the user desired such properties as lightweightness and ease of handling. Further, plastics have been developed which are not only lightweight but are strong such that they have application in those uses where breaking, cracking or splintering are a problem, such as in eyewear. In the United States in 1977, the sales of glass spectacle lenses was estimated at about 40 million pairs as opposed to about 21 million pairs for plastic. It is predicted that in 1982, 30 million pairs of glass lenses will be sold as compared to 40 million pair of plastic lenses.
A certain number of these lenses will be tinted in order to reduce the transmission of light through them. This tintability of the lenses does not seem to be a major problem, since there are a number of tints of varying colors which can be used to tint the lenses. Moreover, the plastics are readily receptive to these tints so that various intensities, as well as various colors of lenses, can be obtained.
Plastic substrates have several major problems, however. Generally, polycarbonates and acrylics are soft, and articles prepared from these plastics scratch or abrade quite readily. Therefore, there has been a great deal of investigation into coatings for such articles in order to enhance the abrasion resistance of the surface of the plastic articles. This problem is particularly acute in plastic lenses and transparent plastic sheeting used in bus, airplane, and train windows and in architectural windows and panels.
One premier coating that has found wide acceptance for such applications is the coating known as the Dow Corning abrasion resistant coating, which is a siloxane based, silica reacted, curable coating especially adapted to give hard surfaces when cured on plastic substrates. This material is disclosed in U.S. Pat. No. 3,986,997, issued Oct. 19, 1976. This material, however, even though having a hard, abrasion resistant surface, has a major drawback. It is not tintable! Therefore, it would be useful to develop an abrasion resistant coating which not only gave enhanced abrasion resistance to these plastic substrates, but it would be extremely useful if the coating was also tintable.
Such coatings have been developed, but they too have some drawbacks. For example, U.S. Pat. No. 4,211,823, issued July 8, 1980, describes the preparation of a tintable coating for use on plastic substrates. The material comprises a hydrolyzate of a silane compound containing at least one epoxy group and not less than two alkoxy groups, fine silica particles and an aluminum chelate compound. This material is tintable but suffers from the fact that it is not exceptionally abrasion resistant, and it has a short resin pot life with a tendency to easily form gel specks.
Another coating system for use on lenses is a material described in U.S. Pat. No. 4,073,967, issued Feb. 14, 1978, as a combination of a reactive silane and a metal cluster. This material is tintable but does not offer the ultimate in abrasion resistance and handleability.
Furthermore, it would be desirable to have an additive for various resins in order to achieve tintability in resins which are not themselves ordinarily tintable.
The silane adducts of this invention help overcome the problems associated with the prior art materials and, in addition, these silane adducts are not volatile under coating curing conditions or in use in the cured coating. As long as the silane adducts are compatible with the curable resin, the adduct will be useful and perform its function therein.